Vacuum exhaust system

ABSTRACT

A vacuum exhaust system can improve the operating efficiency of the vacuum exhaust system while reducing the system cost, to quickly attain a vacuum in the auxiliary chambers without increasing the size of the vacuum pumps. The vacuum exhaust system comprises a first pumping section and a second pumping section disposed downstream of and in series with the first pumping section. A main exhaust passage is provided to communicate a main chamber with a suction port of the first pumping section, and an auxiliary exhaust passage is provided to communicate an auxiliary chamber with a suction port of the second pumping section.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a vacuum exhaust system for usein evacuating a processing chamber for advanced products such assemiconductor devices, for example.

[0003] 2. Description of the Related Art

[0004] A conventional arrangement of a vacuum exhaust system used insemiconductor device manufacturing processes to evacuate a processingchamber for carrying out such process as etching and chemical vapordeposition (CVD) of semiconductor wafers is shown in FIG. 8. A mainchamber (processing chamber) 10 is connected on both sides to auxiliarychambers (load lock chambers) 12 a, 12 b, for loading and unloadingpurposes through respective gates 14. Each auxiliary chamber 12 a, 12 bis isolated from or open to the external environment by a gate 15.

[0005] The main chamber 10 is connected to a vacuum pump 18 through anexhaust path 16 having a valve 20, and each auxiliary chamber 12 a, 12 bis connected similarly to a vacuum pump 24 through an exhaust path 22having a valve 26. It has been customary to use rotary oil pumps for thevacuum pumps 18, 24, but lately, dry pumps are used primarily for thistype of work.

[0006] In this type of apparatus, in order to access the main chamber 10while it is under vacuum, loading or unloading of a workpiece into themain chamber 10 requires that an auxiliary chamber 12 be evacuatedfirst, and the gate 14 opened next so as to avoid exposing the mainchamber 10 to external atmosphere. This is done to prevent the mainchamber 10 and associated piping from contamination as well as toimprove productivity by shortening the time for re-starting.

[0007] In such conventional systems, a vacuum pump is provided for eachchamber to evacuate individual chambers, therefore, working efficiencyof each vacuum pumps is low. If the number of main chambers 10 isincreased in an effort to raise productivity, it leads to a problem thatthe number of vacuum pumps need to be increased, leading ultimately to alarge size facility and higher running costs. If an attempt is made toshorten the time for evacuating the auxiliary chambers, a highercapacity for each pump is required, thus aggravating the above problemseven further.

SUMMARY OF THE INVENTION

[0008] It is an object of the present invention to provide a vacuumexhaust system to enable as much sharing of vacuum pumps as possible, toimprove the operating efficiency of the vacuum exhaust system whilereducing the system cost, or to quickly attain a vacuum in the auxiliarychambers without increasing the size of the vacuum pumps.

[0009] The object has been achieved in a vacuum exhaust system forevacuating a main chamber and at least one associated auxiliary chambercomprising: a first pumping section; a second pumping section disposeddownstream of and in series with the first pumping section; a mainexhaust passage communicating the main chamber with a suction port ofthe first pumping section; at least one auxiliary exhaust passagecommunicating the auxiliary chamber with a suction port of the secondpumping section.

[0010] Accordingly, the main chamber can be evacuated with two pumpingsections arranged in series, and the auxiliary chambers are evacuatedwith one of the pumping sections, thereby increasing the operatingefficiency of each pumping section while keeping the capacity of eachpump as small as practicable.

[0011] The first and second pumping sections may share a common drivemotor. Accordingly, one multi-stage vacuum pump can manage the task ofevacuating an entire processing system so that the number of vacuumpumps can be reduced compared with a case of providing a vacuum pump foreach auxiliary chamber. However, the first pumping section and thesecond pumping section may be provided with individual drive sections.

[0012] The pumping sections may be controlled so as to obtain a minimumfluctuation in pressure, according to a pressure measured inside themain chamber. Accordingly, pressure changes can be held to a minimum inthe main chamber which is an important chamber for processing advancedproducts such as semiconductor devices.

[0013] Another aspect of the invention is a vacuum exhaust system forevacuating a main chamber and a plurality of associated auxiliarychambers, the plurality of auxiliary chambers having a connectingpassage connecting each other which can be opened or closed to equalizepressure in the auxiliary chambers. Accordingly, vacuum environmentpresent inside an auxiliary chambers can be utilized to lower thepressure of another auxiliary chamber which may be at an atmosphericpressure so that evacuation time can be significantly reduced to improvethe operating efficiency of the overall evacuation operation.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014]FIG. 1 is a schematic diagram of a first embodiment of the vacuumexhaust system of the present invention;

[0015]FIG. 2 is a time-chart showing the control steps for the firstsystem shown in FIG. 1;

[0016]FIG. 3 is a schematic diagram of a variation of the first system;

[0017]FIG. 4 is a schematic diagram of another embodiment of the vacuumexhaust system of the present invention;

[0018]FIG. 5 is a time-chart showing the control steps for the secondsystem shown in FIG. 4;

[0019]FIG. 6 is a variation of the second system;

[0020]FIG. 7 is a schematic diagram of a third embodiment of the vacuumexhaust system of the present invention; and

[0021]FIG. 8 is a schematic diagram of a conventional vacuum exhaustsystem.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] Preferred embodiments will be presented in the following withreference to the drawings.

[0023]FIGS. 1 and 2 relate to a first embodiment of the vacuum exhaustsystem of the present invention, which includes, as in the conventionalsystems, a main chamber 10 for carrying out processes such as etchingand CVD of semiconductor wafers. An auxiliary chamber 12 a is attached,through a gate 14 a, to the main chamber 10 on the loading-side, and anauxiliary chamber 12 b is attached, through a gate 14 b, to the mainchamber 10 on the unloading-side. Each of the auxiliary chambers 12 a,12 b is isolated from and connected to the outside atmosphere throughrespective gates 15 a, 15 b.

[0024] To exhaust three chambers 10, 12 a, 12 b, one two-stage pump 34is used. The two-stage pump 34 has a first pumping section 30 a on theupstream side, and a second pumping section 30 b on the downstream side.The pumping sections 30 a, 30 b share a common shaft connected to avariable-speed motor 32. The two-stage pump 34 is provided with asuction port 34 a, and an exhaust port 34 b, and an intermediate port 34c opening at a location between the pumping section 30 a, 30 b. Theexhaust passage 16 for the main chamber 10 is connected through a valve20 to the suction port 34 a, and the exhaust passages 22 a, 22 b,respectively, for auxiliary chambers 12 a, 12 b, are connected thoughrespective valves 26 a, 26 b to the intermediate port 34 c.

[0025] As shown in FIG. 2, performance of the two-stage pump 34 isdesigned so as to enable exhaustion of the main chamber 10 at a firstrotation speed n₁, and to enable exhaustion of the main chamber 10 andone of the auxiliary chamber 12 a, 12 b concurrently at a secondrotation speed n₂ which is larger than n₁. This exhaustion system isprovided with a control section 38 to control the operating parameterssuch as on/off and rotational speed for the variable speed motor 32according to output signal from a pressure sensor 36 provided inside themain chamber 10. Speed control can be effected by following a certainpre-selected pattern in sequence or by feedback control to followsignals output from the sensor 36.

[0026] Operation of the vacuum exhaust system in first embodiment willbe explained with reference to FIG. 2 showing the time-sequence of aprocessing workpiece. First, the gate 15 a is opened to load theworkpiece into the auxiliary chamber 12 a, and the gate 15 a is closed.Next, valves 26 a, 20 are opened and the pump 34 is operated at thehigher second speed n₂, and the rotation speed is gradually reduced backto the first speed n₁ during a time interval (t₁-t₂) so that theauxiliary chamber 12 a and the main chamber 10 are both evacuated. Afterthe main chamber 10 reaches a required pressure, workpiece processingoperation can be started.

[0027] While the processing is proceeding in the main chamber 10, theauxiliary chamber 12 b will also be evacuated. The pump 34 is operatedat the higher second speed n₂ and the rotation speed is graduallyreduced back to the first speed n₁ during a time interval (t₂-t₃). Afterthe auxiliary chamber 12 b is exhausted, the pump 34 is operated at thefirst speed n₁ to complete the processing in the main chamber 10 duringa time interval (t₃-t₄).

[0028] Next, the gate 14 b is opened to unload the processed workpiecefrom the main chamber 10 to the auxiliary chamber 12 b at time t₄.During the processing interval in the main chamber 10, a new workpieceis placed inside the auxiliary chamber 12 b by opening the gate 15 a, sothat the interior pressure is at an atmospheric pressure. At this point,the steps from time t₁ are repeated. In the meantime, the gate 15 b isopened to remove the processed workpiece from inside the auxiliarychamber 12 b.

[0029] By following the steps described above, the embodied exhaustionsystem enables to operate the system with one pump by suitably switchingthe evacuation process among the main chamber and the auxiliary chambersthereby reliably maintaining the required load locking functions. Andsince the emphasis is placed on exhausting the main chamber by using amulti-stage pump, lowering of gas exhausting capability of the mainchamber is avoided.

[0030] In the above case, although the rotation speed was controlledsequentially according to a pre-determined pattern, it is permissible touse a feedback control according to signals output from a pressuresensor 36. When valves 26 a, 20 are opened to evacuate the auxiliarychamber 12 a and the main chamber 10, opening of the valve 26 a causesthe pressure in the mid-chamber 35 of the pump 34 to increase, and thepump capacity is lowered so that the interior pressure in the mainchamber 10 is also increased. To avoid such critical pressurefluctuation in the main chamber 10, the interior pressure can bemonitored by a pressure sensor 36 so as to control the rotation-speed ofthe pump 34 at a speed between the second speed n₂ and the first speedn₁.

[0031]FIG. 3 shows a variation of the first embodiment, which uses twoindividual pumps connected in series. A first stage booster pump 42 isconnected in series with a second stage main pump 46. Each pump isdriven by separate variable speed motors 40, 44, whose speeds can becontrolled separately by a control section 38.

[0032] The exhaust passage 16 of the main chamber 10 is connectedthrough a valve 20 to a suction port 42 a of the booster pump 42, andthe exhaust port of booster pump 42 and the suction port of main pump 46are connected through a connecting pipe 50 having an intermediate port52. The exhaust passages 22 a, 22 b of the auxiliary chambers 12 a, 12 bare connected through the valves 26 a, 26 b to the intermediate port 52.Operational characteristics of this embodiment system are the same asthose in the first case, and their explanations will be omitted.

[0033] In this example also, the rotation speed of the pump can befeedback controlled using the output signals from a pressure sensor 36.In this example, rotation speed of main pump 46 and booster pump 42 canbe controlled independently to enable more precise control of thepressure.

[0034]FIG. 4 is a schematic diagram of another embodiment of the vacuumexhaust system. This system includes: a connecting passage 60 to connectboth auxiliary chambers 12 a, 12 b shown in FIG. 1 to equalize thevacuum pressure; and a valve 62 for opening or closing the connectingpassage 60. The valve 62 is controlled by a control section 38 to openin advance when either the auxiliary chamber 12 a or 12 b is exhausted.

[0035] The embodied vacuum exhaust system is used, for example, whenexhausting the auxiliary chamber 12 a after it has been loaded with aworkpiece so that it is at an atmospheric pressure, in a way that thevalve 62 is opened before the valve 26 a is opened to evacuate with themulti-stage pump 34 (at time t₅). At this time, the auxiliary chamber 12b has a processed workpiece passed from the main chamber so that itsinterior pressure is maintained at some low pressure. Therefore, byopening the valve 62, air flows from the auxiliary chamber 12 a toauxiliary chamber 12 b so that both chambers attain a common pressureintermediate between an atmospheric pressure and vacuum.

[0036] After this stage, valve 62 is closed, and as in FIG. 1, pump 34is operated at a higher second speed n₂ (at time t₆) to exhaust bothauxiliary chamber 12 a and main chamber 10. In this case, because theinitial pressure in the auxiliary chamber is less than an atmosphericpressure, the length of time required to exhaust the auxiliary chamberis reduced compared with the system shown in FIG. 1. In the auxiliarychamber 12 b, gate 15 b is opened and the processed workpiece iswithdrawn. This system thus allows to utilize the reduced-pressureenvironment of the auxiliary chamber 12 b, which is normally discardedto waste, to shorten the evacuation time of the auxiliary chamber 12 a.This feature further contributes to increasing the operating efficiencyof the overall vacuum exhaust system.

[0037] Similarly, when exhausting the auxiliary chamber 12 b, valve 62is first opened temporarily (time t₇) to introduce the vacuumenvironment in the auxiliary chamber 12 a before an unprocessedworkpiece has been loaded into the auxiliary chamber 12 b (time t₇-t₈)so that auxiliary chamber 12 b can be reduced in pressure, and then themulti-stage pump 34 is operated at a fast speed. Thus, the exhaustiontime for the auxiliary chamber 12 b can be shortened.

[0038]FIG. 6 shows a variation of the system shown in FIG. 4. Thissystem is based on the variation based on the third embodiment shown inFIG. 3, and includes a connecting path 60 and a valve 62 which isdesigned to be opened before evacuating either of the auxiliary chamber12 a or 12 b.

[0039]FIG. 7 shows a third embodiment, and includes auxiliary chambers12 a, 12 b having dedicated exhaust passages 22 a, 22 b, provided withrespective vacuum pump 24 a, 24 b respectively, connected withconnecting passage 60, and within the connecting passage 60, a valve 62which is designed to open prior to evacuating either auxiliary chamber12 a or 12 b. This system also enables to utilize waste vacuum, as inthe systems shown in FIGS. 3 and 6, to shorten the exhaustion timerequired to evacuate the auxiliary chambers 12 a, 12 b.

What is claimed is:
 1. A vacuum exhaust system for evacuating a mainchamber and at least one associated auxiliary chamber comprising: afirst pumping section; a second pumping section disposed downstream ofand in series with said first pumping section; a main exhaust passagecommunicating said main chamber with a suction port of said firstpumping section; and at least one auxiliary exhaust passagecommunicating said auxiliary chamber with a suction port of said secondpumping section.
 2. A vacuum exhaust system according to claim 1 ,wherein said at least one auxiliary exhaust passage comprises a shut-offvalve.
 3. A vacuum exhaust system according to claim 1 , wherein saidfirst pumping section and said second pumping section share a commondrive motor to constitute a multi-stage vacuum pump.
 4. A vacuum exhaustsystem according to claim 1 , wherein said first pumping section andsaid second pumping section are individually provided with respectivedrive sections.
 5. A vacuum exhaust system according to claim 1 ,further comprising a control section for controlling rotation speed ofsaid first or second pumping sections so as to obtain a minimumfluctuation in pressure, according to a pressure measured inside saidmain chamber.
 6. A vacuum exhaust system according to claim 1 , whereinsaid a plurality of said auxiliary chambers are provided to said mainchamber.
 7. A vacuum exhaust system according to claim 1 , wherein saidauxiliary chamber is a load lock chamber.
 8. A vacuum exhaust system forevacuating a main chamber and a plurality of associated auxiliarychambers, said plurality of auxiliary chambers having a connectingpassage connecting each other which can be opened or closed to equalizepressure in said auxiliary chambers.
 9. A vacuum exhaust systemaccording to claim 8 , wherein said auxiliary chambers comprise at leastone load lock chamber.
 10. A vacuum exhaust system according to claim 8, further comprising a control section for controlling said connectingpassage to open and close before one of said auxiliary chambers areevacuated.
 11. A method for exhausting a main chamber and at least oneassociated auxiliary chamber comprising: disposing a second pumpingsection downstream of and in series with a first pumping section;communicating said main chamber with a suction port of said firstpumping section through a main exhaust passage; communicating said atleast one auxiliary chamber with a suction port of said second pumpingsection through an auxiliary exhaust passage; and opening said auxiliaryexhaust passage so as to apply evacuation ability of said second pumpingsection to evacuation of said auxiliary chamber.
 12. A method accordingto claim 11 , wherein said first pumping section and said second pumpingsection share a common drive motor to constitute a multi-stage vacuumpump.
 13. A method according to claim 11 , wherein said first pumpingsection and said second pumping section are individually provided withrespective drive sections.
 14. A method according to claim 11 , furthercomprising controlling rotation speed of said first or second pumpingsections so as to obtain a minimum fluctuation in pressure, according toa pressure measured inside said main chamber.
 15. A method according toclaim 11 , wherein said a plurality of said auxiliary chambers areprovided to said main chamber.
 16. A method according to claim 11 ,wherein said auxiliary chamber is a load lock chamber.